Blades and devices for cutting tire cord fabrics are described in U.S. Pat. No. 5,423,240 issued to Robert P. DeTorre, the inventor herein, and incorporated herein by reference. The cutting or slitting of cord reinforced, calendered uncured elastomeric tire fabric continues to become a more difficult task with advances in tire design. Although the uniformly spaced parallel cords may be made from small diameter strands of nylon, polyester, or aramid fibers, the most popular and most difficult fabrics to cut continue to be those reinforced with steel cord. The steel cords, whether individual filaments, twisted multiple filaments, or mixtures of the two continue to become smaller and harder and more difficult to cut. Adding to the difficulty is the movement to sharper or smaller angles of the bias cut of the fabric. The angles now may be as little as 5 degrees. This results in longer cuts through the fabric sheet and longer cuts through individual filaments. Increases in tire tread widths also require longer cuts of the sheets. The blades, used to cut the fabric, overlap and the harder smaller filaments cut at smaller angles can be trapped between the overlapping blades resulting in torn filaments instead of clean cuts and/or smearing of the uncured elastomeric foundation of the fabric.
A variety of equipment is used to cut tire fabric. The equipment includes two circular blades that are also called discs or wheels, and a circular blade with an anvil or bar. The rotating circular blades and the disc and anvil equipment typically include air cylinders to impose opposing forces on the paired blades to force them together during the cutting operation. Another variety of equipment employs long rigid shear blades or guillotine blades. This equipment uses one stationary blade and one moving blade. The equipment is similar to the perhaps more familiar metal shears where a hydraulically operated blade moves up and down in a vertical plane essentially parallel to the stationary blade. The long moving blade may instead be mounted on a hydraulically operated radial reciprocating arm so the two blades are not essentially in a vertical plane until the arm moves the blade into contact with the stationary blade. These paired bar beam blades overlap each other in the cutting process and employ blade inclination pinch angles of about 1 to 4 degrees. The inclination angles are in the vertical plane and apparent in front views of the blades. The blades are essentially parallel in the horizontal plane with little or no crossover pinch angle. Small gaps or interferences provide the cutting point. The crossover pinch angle is the angle visible in top views of the blade. If the blade is cambered, it may have a very small crossover angle over the first half of a cut and a negative crossover angle after the center of the cut. A camber of 0.005 inches over an 80 inch blade gives a minute or insignificant pinch angle of about 0.003 degrees. The camber is intended to compensate for the machine deflection of the long blade rather than provide a cutting pinch angle.
The cutting point moves progressively from one end of the blades to the opposite end of the blades. The shear blades may be about 5 meters or about 16 feet in length or longer. They are mounted on equally long rigid blade holders. The blade holder may have a camber or arch so that a snugly fit blade will have the camber of the holder. The holder may, for example, be a 3 inch by 3 inch steel bar with numerous bolts along the length of the bar pulling the blade up against the holder. Jackscrews or push-pull bolts may be used to not only provide the initial camber to the blade but also to correct the blade camber after repeated use. The jackscrews or push-pull bolts may also be used to mount blades without a camber so the moving blade is essentially parallel to the stationary blade. These bolts may also be used to correct misalignments or wear after use. Both initial and corrective alignments are time consuming and labor intensive. Sometimes the actual incremental cutting of very thin paper is used to check and adjust the horizontal alignment of the blades. When cutting is occurring at one end of the blades the other end of the blades may be as much as 4 inches apart in the vertical plane. Periodic adjustments require periodic down times if quality cuts are to be maintained. Of the different blades in use in various tire fabric cutting equipment, the long rigidly mounted bar blades are subjected to the highest repetitive dynamic stresses. These stresses cause localized blade fractures and poor quality cuts. Particularly when the cutting edges become dulled, greater stresses are created not only on the blades as they hammer on each other but also on other elements of the machine. The side crowned tungsten carbide blades described in U.S. Pat. No. 5,423,240 have been successfully used in all of the described equipment, including the most dynamically stressed rigid blades, in 5 meter lengths. There is some reluctance, however, to use any carbide blade, not just the side crowned blade, because they are all considered to be brittle and subject to fracture. It would be most desirable to reduce the stresses on the long rigid cutting blades and on the other blades employed in cutting tire fabrics as well, not only because of the wear and tear on the blades themselves but also to reduce the wear and tear on bearings, gears, and other parts of the equipment.